document remaining color options

diff --git a/barcat b/barcat
index 9e78016da65ae77b843d876d1702823a2052a5a2..995f66942b0bd7200342b934bf81345a6b47a3de 100755 (executable)
--- a/barcat
+++ b/barcat
@@ -448,6 +448,11 @@ or alternatively I<1;30> for bright black.
 In case of additional colors,
 the last is used for values equal to the maximum, the first for minima.
 If unspecified, these are green and red respectively (I<31 90 32>).
+Multiple intermediate colors will be distributed
+relative to the size of values.
+
+Predefined color schemes are named I<whites> and I<fire>,
+or I<greys> and I<fire256> for 256-color variants.
 
 =item --spark[=<characters>]